The present invention relates to an apparatus for controlling pressure in an ink reservoir of an ink jet printer. The present invention also relates to an ink jet printer including a printhead with an ink reservoir containing liquid ink and a gas volume above the level of the ink. The present invention further relates to a method for controlling pressure in an ink reservoir of an ink jet printer.
An ink jet printer typically contains printheads having one or more nozzle arrays and an ink reservoir from which liquid ink is supplied to the nozzles of the nozzle arrays, so that ink droplets may be ejected from the nozzles by thermal or piezoelectric action, as is generally known in the art. When the level of ink in the ink reservoir is higher than the level of the nozzles, the ink reservoir should be maintained at subatmospheric pressure in order to avoid ink from leaking out through the nozzles. Since the difference between the internal pressure in the ink reservoir and the atmospheric pressure has an influence on the process of droplet generation and hence on the quality of the printed image, it is desirable to keep this pressure difference constant. However, since the internal pressure in the ink reservoir may vary in response to changes of the ink volume contained therein, thermal expansion and the like, it is necessary to control the internal pressure in the ink reservoir.
It is common to apply pressure regulating valves coupled to a pump for allowing compensation of an excessive pressure drop monitored by the detecting means in order to maintain the under pressure in the ink reservoir within a certain predetermined pressure range. Pressure regulating valves however are commonly, relatively expensive and sensitive. Thus, relatively large membranes are required to achieve a relatively high degree of precision in the regulation of the pressure within the ink reservoir. Furthermore, commonly other critical components are required, often resulting in a relatively high mutual friction and are therefore often subjected to a considerable amount of wear. Rubber parts commonly used in the known apparatus to control the pressure within the ink reservoir become fatigued relatively quickly, resulting in a decreased capacity to counteract loads during operation of the apparatus. Thus, the known device is, from a constructive point of view, relatively complex and hence, relatively expensive. Moreover, the components used in the known device are commonly subjected to a considered amount of wear during operational use.